The present invention relates generally to induction type electrical wire preheaters and more particularly to an induction type electrical wire preheater which can be set up to handle intermediate diameter wires or set up to handle small diameter wires and which can be easily switched back and forth from one wire setup to the other to satisfy changing production requirements.
As used herein, the term "intermediate diameter wires" refers to wires having diameters between about 0.101 inches to about 0.032 inches and the term "small diameter wires" refers to wires having diameters between about 0.025 inches to about 0.01 inches.
Induction type wire preheaters are well known devices used extensively in the insulated wire manufacturing industry for preheating wire or cable which is being fed into an extrusion die. In such devices, the wire being heated acts as the moving secondary of a transformer and the primary voltage is used to control the wire temperature.
In U.S. Pat. No. 3,117,209 to W. L. Peltier there is disclosed an example of an induction type electric wire preheater. The preheater includes an upper wheel of predetermined size and made of conductive material, a lower wheel of the same size as the upper wheel and positioned below the upper wheel and an inductor (i.e. transformer), with the inductor being positioned between the two wheels. The inductor includes two vertical spaced apart insulated passageways, with the distance between the two passageways being equal to the diameter of the wheels. In use, the wire being heated enters the device from one side, passes over the upper wheel, down through one of the passageways in the inductor and under the lower wheel, up through the other passageway in the inductor, over the upper wheel again and then exits the device through the other side. Since the distance between the two passageways is fixed, the diameter of the upper wheel is also fixed. This is a limiting factor for production flexibility since the size of the upper wheel used with small sized wire is usually made much smaller than the size of upper wheel used with intermediate sized wire to minimize heat losses at the wheel itself.
One way that has been proposed in the past to avoid the problem associated with the need to use different sized upper wheels to accommodate different wire diameters is to provide two separate preheaters, each having its own uniquely sized upper wheel one preheater for use with intermediate sized wires and the other preheater for use with a smaller sized wires. As can be appreciated, this approach is economically undesirable.
In U.S. Pat. No. 3,176,111 there is shown an adapter which serves as a replacement for the upper wheel on the preheater shown in U.S. Pat. No. 3,117,209 when small size wire is being run. The adapter comprises a plate on which is rotatably mounted an upper wheel and an idler wheel, the upper wheel on the plate being sized smaller than the upper wheel which is being replaced. When the plate is mounted on the preheater in place of the normal upper wheel, the left edge of the idler wheel is vertically over the left passageway of the inductor and the right edge of the replacement upper wheel is vertically over the right passageway. Wire enters the preheater from the left and exits the preheater from the right. Although the attachment serves to reduce the heat loss in the upper wheel when small diameter wires are being run by using a smaller sized upper wheel and also by flattening the angle at which the wire contacts the upper wheel on leaving the inductor, it does not solve the problem of heat loss in the wire in air as it moves from the upper wheel to the extrusion die. The reason for this is that the distance from the wire contact area of the upper wheel on the attachment to the extrusion die is not appreciably less than the distance from the wire contact area of the upper wheel being replaced to the extrusion die. In both cases, the upper wheel is positioned to the left of the right passageway in the inductor. As is known, for small (i.e. fine) wire, the heat loss in air is extremely large. Consequently, any reduction in the distance the wire must travel from the upper wheel to the extrusion die will produce a reduction in this type of heat loss.
Accordingly, it is an object of this invention to provide a new and improved induction type electrical wire preheater.
It is another object of this invention to provide a preheater as described above which can be set up to handle intermediate size wire or set up to handle small size wire and which can be easily switched back and forth from one wire set up to the other to meet changing production requirements.
It is still another object of this invention to provide a preheater which is designed to handle two different sized upper wheels.
It is a further object of this invention to provide a preheater as described above which is designed specifically to reduce heat losses in air when handling small diameter wires.
It is still a further object of this invention to provide a preheater as described above which includes a new and novel type of inductor construction.
It is yet still a further object of this invention to provide a preheater as described above which is simple in construction and easy and economical to manufacture and assemble.